The preparation of Meldrum's acid (originally described as a .beta.-lactonic acid from acetone and malonic acid, also known as diisopropylidene methylene dimalonate; 2,2-dimethyl-1,3-dioxane-4,6-dione; or malonic acid cyclic isopropylidene ester) was first reported by Meldrum in 1908 (see Meldrum, A.N., J. Chem. Soc. 93, 598-601 (1908)). Meldrum's acid is useful as an intermediate for preparing a wide variety of products (see McNab, H., Chem. Soc. Rev. 7 (3), 345-358 (1978)). A specific example of where Meldrum's acid has been shown to be useful can be found in U.S. Pat. No. 4,065,440 in which Meldrum's acid is shown to be useful in a process for increasing the molecular weight of polyesters.
Known methods for preparing Meldrum's acid result in poor yields, typically less than 50 percent (see, for example, U.S. Pat. No. 4,065,440, Example I). A process giving a poor yield of Meldrum's acid is, for many purposes, economically unacceptable.
The present invention is directed to a process which provides significantly improved yields of Meldrum's acid as compared to processes taught in the prior art.